It seems this has become something of a tempest in a teacup. As I mentioned in an earlier post, I believe much of the energy of the dispute has developed over differences in terminology. First, in the vast majority of cases, I agree with Mr Ritchey. In the twenty five years or so I've been involved in EMC, I've never seen the radiation from surface trace fail a product. That said, I've only worked on old/slow boards with fundamental clocks less than 1.5 GHz, although I've worked with 900 MHz intentional radiators to their 10th harmonic. Rules of thumb only work until the thumb is too fat to see the problem underneath it. As I mentioned in an earlier post, resonant patch antennas and other intentional radiating pcb structures are nothing more than fat, well designed traces. Somewhere between them and our ideal EMC designs lies practicality. As frequency increases, I find myself needing increasingly closer inspection of detail. In somewhat oblique support of Mr. Ritchey, most failing EMC issues I've observed have been associated with L di/dt induced voltages on the reference plane caused by surface traces. I/O cables, using said poorly controlled reference planes out to the world, are often a major emissions issue, but that is entirely another subject for discussion. Finally, I believe Mr. Ritchey is correct, but using the following assumptions: - The trace structure and geometry does not approach a resonant structure at the fundamental or appreciable harmonics of the operating frequency. - The reference plane structure supporting the return currents of the surface trace does not significantly contribute to reference plane resonance and induced voltage on attached cables. Respectfully, Brent DeWitt -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey Sent: Sunday, October 19, 2003 6:06 PM To: Larry Barnes; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? I downloaded a copy of this paper a few minutes ago. The conclusions of the paper do not state that microstrip traces emit significant EMI. All that is stated is that the analysis and chamber measurements agree within measurement accuracy of what little energy is detected. The actual amount is not stated in the paper. There is certainly no claim that the detected emissions are large enough to cause concern among EMC engineers. This is likely one of those cases where the difference is between detectable and significant. There is no claim in this paper that the emissions are significant, only detectable. If we are to accept that surface traces are significant sources of EMI, there needs to be credible demonstration of this. The reason is, designers are expected to expend cost avoiding microstrip traces. To do this, there needs to be demonstrated emissions that are worth the extra cost to control. My challenge to the proponents of this claim is to provide this demonstration. I and many others have designed hundreds, maybe thousands of PCBs with traces on outer layers with all the products successfully passing all emissions tests. That could not happen if these claims are true. Lee > [Original Message] > From: Larry Barnes <larry.barnes@xxxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Date: 10/18/2003 5:42:14 AM > Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > I just couldn't resist after all this discussion. I would refer you to = > a study done by Dr. Dave Hill of NIST. I demonstrates that microstrips = > indeed radiate. The title of the paper is "Radiated Emissions and = > Immunity of Microstrip Transmission Lines: Theory and Reverberation = > Chamber Measurements" IEEE Trans on EMC May 1996.=20 > > Larry > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > Lawrence C. Barnes > QLogic Corporation > Aliso Viejo, CA 92656 > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu